Low and medium voltage, high current circuit breakers generally include a charging mechanism or energy storage device for developing the relatively large force needed to close the breaker. The energy is generally developed by loading a spring through some form of motor means or a manually operated charging handle. The charging mechanism generally includes a pair of heavy extension coil springs that are incrementally loaded (stretched or compressed) by the camming action of a lever that is driven by a ratchet and pawl arrangement. The charging or closing springs are loaded by rotating the ratchet to force a lever arm (and the spring) over center, where they are secured by a latch. The breaker contacts are closed by tripping the latch to discharge the closing springs.
There is a need for a mechanism which incrementally unloads the charging mechanism so that the electrical contact operating mechanism is closed slowly. This allows maintenance and lubrication of the operating mechanism, adjustment of contact pressure settings, monitoring of the contact closing sequence, and testing of the overall mechanical operation of the circuit breaker before it is energized. A slow close mechanism also allows functionally monitoring the timing of the auxiliary switches and control devices.
The prior art provides gagging devices which are attached to the closing springs to allow their partial discharge. One problem with these gagging devices is that there insertion is time-consuming and cumbersome, often requiring an operator to work in tight quarters. Once the maintenance on the circuit breaker is complete, the gagging device must be removed and the charging mechanism reset. Inadvertently leaving a gagging device in the circuit breaker while it is energized could result in severe damage to the breaker and possible injury to the operator. Failure to reset the charging mechanism leaves the circuit breaker operating in an unsafe manner.
There is a need for a slow close mechanism which is made an integral part of the circuit breaker to eliminate time-consuming attachments. Preferably, the slow close mechanism prevents inadvertent operation of the circuit breaker by automatically resetting the charging mechanism.